Someone has been arguing with me about fellowship and they say it is okay to have meals together in the building because eating together is an expression of fellowship. He says, "If eating together and having fun together is not an expression of fellowship, then what is it?" He says we do these things together because we are in fellowship.
How do I answer him?
Your friend does a little bit better than most by avoiding calling meals fellowship. Instead he is arguing that if something expresses fellowship, then it is authorized.
To illustrate the flaw in the argument, let's talk about worship. If something can be classified as an expression of worship, does that make it authorized? Those who use instrumental music would like to argue in this way. After all the Israelites used instrumental music in their worship (Psalm 150). But why stop there? People used self-mutilation in their worship of Baal (I Kings 18:28). Does the fact that something can be called an expression of worship make it authorized? I hope you see that the answer is clearly "No!"
Your friend made several mental leaps in his argument. He argued that eating together is an expression of fellowship. That is true. "So continuing daily with one accord in the temple, and breaking bread from house to house, they ate their food with gladness and simplicity of heart" (Acts 2:46). People who are in fellowship often share meals together. That is why when a person is withdrawn from, sitting down to eat with them is forbidden (I Corinthians 5:11). But where is the authority for the church to provide meals or facilities to those in fellowship? The only meal that is commanded of the church to share is that of the Lord's Supper (I Corinthians 10:16-17). Thus your friend took individual acts done voluntarily and made them into a required church activity without proving that God authorized it.